Heat treatment furnaces of a hot air circulating type and a multistage-hearth rotation type have been used to apply heat treatment to heating targets such as an aluminum alloy, for example. The former hot air circulating type has an advantage of reducing a temperature variation inside a furnace, while the latter multistage-hearth rotation type has an advantage of saving a space of a heat treatment facility.
The applicant of the present application has filed a patent application involving a rotary heat treatment furnace in which the hot air circulating type is combined with the multistage-hearth rotation type (refer to Japanese Unexamined Patent Publication No. 2011-7471, for example).
As illustrated in FIG. 4, the rotary heat treatment furnace 10 includes a furnace body 11 incorporating a housing rotary body 12 provided with housing chambers 12a and a central portion 12b. The furnace 10 also includes hollow chambers 70 that correspond to the respective housing chambers 12a. Hot air fed to the central portion 12b from thereabove is supplied to all heating targets 100 through the hollow chambers 70.
The rotary heat treatment furnace 10 disclosed in Japanese Unexamined Patent Publication No. 2011-7471 is such that the hot air for heating the heating targets 100 is not priory used to heat objects other than the heating targets 100. Thus, the hot air supplied to each of the heating targets 100 has a substantially same temperature, whereby all the heating targets 100 can be heated evenly.
Other than the furnace described above, another style of rotary heat treatment furnace is disclosed that supplies hot air to heating targets 100 from therebelow (refer to Japanese Unexamined Patent Publication No. 2004-257658, for example).
As illustrated in FIG. 5, this rotary heat treatment furnace 20 includes a fan 24 provided to an upper part of a central portion thereof. Hot air is first sent by the fan 24 to the bottom of the furnace, and is fed to a housing chamber 22a at the lowest position and consecutively to a housing chamber 22a at the highest position. The hot air passed through the highest housing chamber is again sent to the bottom of the furnace by the fan 24.